High definition television (HDTV) is now being introduced commercially in the U.S. Many U.S. television stations broadcast high definition television programs, and HDTV receiving equipment is available to the consumer. HDTV is a type of digital television (DTV). This means that the signals are transmitted generally in digital format, requiring special receivers. Two HDTV formats, approved in the United States, referred to as 1080i and 720p. The 1080i refers to a television picture with 1,080 video scan lines each with 1,920 pixels horizontally. The i refers to interlace scanning as used in traditional analog (NTSC, PAL, SEC AM) television which alternates sending odd lines and even lines in each frame to form a field. The 720p format provides a pictures with 720 vertical lines each with 1,280 pixels horizontally. The p refers to progressive scanning as used in computer displays. HDTV is replacing standard analog (NTSC, in the U.S.) television. HDTV is also being introduced outside the United States although similar to the case with analog television, somewhat different HDTV formats are being adapted by different countries and groups of countries, e.g., using different frame rates. Digital TV here refers to particular television formats and is not the same as so-called digital cable television. Digital TV (in this sense, actually digital broadcast television) actually defines (in the U.S.) eighteen different formats for broadcast television in a digital format. HDTV is six of those eighteen formats. The U.S. Federal Communications Commission (FCC) has ordered that by May 2006 all U.S. broadcasters will broadcast digital television signals in place of analog television signals.
As well known, in analog (e.g. NTSC) television, each video (horizontal) scan line includes a horizontal blanking interval including what is called a horizontal synchronization (sync) pulse. In between the horizontal blanking intervals there occurs what is called the active video. The end of each field of video also includes a vertical blanking interval. The blanking intervals are used to provide timing signals for the picture and operation of the receiver. The well known horizontal synchronization pulse in analog television includes what is called a front porch immediately preceding the horizontal sync pulse and a back porch immediately following the horizontal sync pulse. In analog television such as NTSC, PAL, and SECAM television the horizontal back porch also contains the color burst which is a color timing reference signal.
The vertical blanking regions are considerably longer than the horizontal blanking intervals in analog television and extend over, in terms of duration, the equivalent of a number of horizontal scan lines. The vertical blanking interval includes a relatively long vertical synchronization pulse followed by a number of so called equalizing pulses. In analog television, the horizontal sync pulse includes only two levels, one of which corresponds to a zero amplitude pulse or a blanking level and the other which is a lower amplitude pulse which is at sync tip level. However, for HDTV there has been defined an additional third level of the sync pulse, thus providing what is called a tri-level horizontal sync pulse. This includes initially a low negative going pulse (e.g. a sync tip level), followed immediately by a high positive going pulse, which crosses a blanking level. Thus the three levels provided are low, high and blanking level. The positive going pulse in a tri-level sync pulse is higher than the blanking level. Hence the use of tri-level sync pulses is conventional in HDTV as defined in the United States and also as used in other countries. Note that the HDTV typically includes three channels and hence is a type of composite video. These channels, for example, are referred to as Y (luma), Pb and Pr (chroma) which are the chroma channels. The Y (luma) channel is also sometimes referred to as the green channel with Pb sometimes referred to as a blue channel and Pr as a red channel. Of course other types of multiple channel video systems can be used.
Note that while the signal transmission in HDTV is digital, actually a significant portion of the signal processing takes place effectively in the analog domain and hence it is conventional to draw waveforms of the video signal for HDTV which look essentially the same as the analog type waveforms drawn to represent analog television signals. That convention is followed here.
One exemplary tri-level sync pulse used in HDTV has the blanking level at zero volts, the negative going portion at −0.3 volts and the positive going portion at +0.3 volts, followed by a back porch region and then followed by the active video portion. Just as in analog television, this tri-level horizontal sync pulse is repeated every scan line to create an entire high definition video frame. Synchronization and loss of synchronization otherwise may operate somewhat differently in high HDTV than in analog television. For analog television, loss of synchronization causes the image to roll and distort on the screen as the TV set tries to relock back into sync. However, high definition television receivers, being essentially digital devices, may have a different operation. On the screen, when sync is lost, in one example, there is likely to be displayed a green flash in the image or a series of green frames for ongoing loss of synchronization. In another example, a loss of sync in an HDTV signal may cause the display to blank out.
Also well known in the field of analog video and television is what is generally referred to as content management, an aspect of which is copy protection. Examples of copy protection are disclosed in Ryan U.S. Pat. No. 4,631,603 and Ryan U.S. Pat. No. 4,577,216 both incorporated herein by reference in their entireties. Generally these describe methods and apparatus for processing a video signal to inhibit making of acceptable video recordings therefrom. It is also known to defeat these copy protection processes, see for instance Ryan U.S. Pat. No. 4,695,901 also incorporated by reference herein in its entirety. Another method of inhibiting making of acceptable video recordings is disclosed in Ryan U.S. Pat. No. 4,819,098 using clustering modifications to a video signal. Generally these copy protection techniques and apparatus modify an otherwise standard video signal in such a way that the resulting video signal, while readily displayed on a display device (a TV set or monitor) when provided to a video recorder such as a video tape recorder, produce distortion on any copies made therefrom by the recorder, thus resulting in an unacceptable copy in terms of later viewing. Copy protection in this context includes a technical means for making copies unviewable or less viewable on a conventional display device when using a conventional recording device to make the copies.
The broader field of content management also includes so-called compliant devices which are designed so that they include circuitry that detects for certain signals or the absence of same in a video signal being received. The presence (or absence) of the particular signal acts as a command to the receiving device thereby to enable or inhibit recording. In some cases, this involves generational copy management whereby a first generation copy may be made, but subsequent generation copies are prevented. See for instance Talstra et al. U.S. Pat. No. 6,701,062 disclosing such a system for video as provided on a media such as a DVD. Such copy management is applicable to a digital video signal of the type used on video media such as DVDs. These more sophisticated copy control systems typically require dedicated circuitry and/or software in the receiving device to detect and interpret the special data provided in the video signal for purposes of content management.
However, none of these methods are directed to HDTV or, for that matter, to digital broadcast television generally. In this context, of course, broadcast includes not only conventional broadcast, but also cable, satellite broadcast, etc. None of these methods address the particular configuration of HDTV video signals or the differences of HDTV from, for instance, analog television signals.